Printing form attachment means

ABSTRACT

A printing form attachment device is provided for removably attaching a flexographic printing form made of a photopolymeric material by adhesion on a plate cylinder of a printing press. The printing form attachment device includes a completely exposed photopolymeric printing form attachment layer (3) made of a photopolymeric material located on the plate cylinder (7) for removable adherent attachment of the printing form to the plate cylinder utilizing the adherent and sticky characteristics of the photopolymeric material. A flexible support layer (2) is provided which supports the photopolymeric printing form attachment layer (3).

This invention relates to a printing form attachment means for removablyattaching a flexographic printing form by adhesion on a plate cylinderof a printing press, more particularly for removably attaching aprinting form of photopolymeric material.

The known printing form attachment means of this type (EP 0 313 510)comprises a strip of double-sided adhesive tape, e.g. supplied from aroll, which is attached with one adherent side on the plate cylinder sothat on the other adherent side one or more flexographic printing formscan be attached.

Flexographic printing forms consist of a photopolymeric layer attachedto a support layer. Through a film, on which the desired images and/ortext etc. have been recorded, the photopolymeric layer is exposed andthen washed out, whereafter finally the resulting printing form issubjected to a subsequent treatment.

Reference is made to U.S. Pat. No. 3,210,187 which relates tophotopolymeric elements such as printing plates with relief structuresas well as processes for making the same.

In case of using the known printing form attachment means the problemarises that the support layer of the printing form adheres strongly tothe adherent layer of the double-sided adhesive tape which serves asprinting form attachment means, due to which removal of the printingform from the plate cylinder is troublesome and moreover a residual partof the adhesive layer often remains on the printing form. Consequentlythe printing form attachment means generally has to be replaced afterhaving been used one or several times, whereas on the other hand theprinting form has to be cleansed in order to remove the adhesivematerial. Because the cleansing operation of the printing form isintensive the printing form is commonly thrown away. Thus in case of arepeat order a new printing form has to be produced.

It is an object of this invention to provide a printing form attachmentmeans of the type as mentioned in the preamble, which overcomes thesedisadvantages in a simple, but nevertheless effective way.

In accordance with the invention the printing form attachment means ischaracterized in that the printing form attachment means utilizes theadherent and sticky characteristics of a photopolymeric material in thatit comprises a completely exposed photopolymeric printing formattachment layer for the removable adherent attachment of the printingform on the plate cylinder as well as a flexible support layer whichsupports the photopolymeric printing form attachment layer.

The invention relies on the recognition that in order to obtain aparticularly effective printing form attachment means advantageously theadherent characteristics of a photopolymeric layer can be utilized.Experiments have shown that these adherent characteristics aremaintained in case of intensive use during a period of at least 8 to 12months. Moreover, on the one hand a good attachment of the printing formon the plate cylinder is realized, whereas on the other hand theprinting form can relatively easily be removed from the adherentphotopolymeric printing form attachment layer and no residualphotopolymeric material remains on the printing form. This results in along lifetime of the printing form attachment means applied to the platecylinder, whereas on the other hand the printing form no longer needs toundergo a cleansing operation. Damaging of the printing form by theremoval is excluded as well, so that the printing form is availableseveral times for repeat orders without any problem.

Moreover, the printing form attachment means of the invention has theadvantage that the photopolymeric layer is highly resistant to thesolvents present in the used inks. A further important advantage isachieved in that the photopolymeric layer as compared with the adherentadhesive layers of the known double sided adhesive tape has aconsiderable thickness of 1-4 mm and a relatively low hardness andpreferably is of at least 1.5 mm in thickness. In this way thephotopolymeric layer of the printing form attachment means forms a kindof resilient layer between the printing form and the plate cylinder,which results in taking away the unavoidable non-circular shapes of theplate cylinder and printing forms and tolerance due to gear abrasion bythe photopolymeric layer. This aspect induces a considerable lifetimeincrease of the moving parts of the printing press, as well as lifetimeincrease of the printing form. An accompanying important advantage isthat the thickness of the printing form itself can be considerably lessthan the required thickness, because of the fact that the relativelythick photopolymeric layer of the printing form attachment means alreadyprovides an important part of the required total height of the printingthickness above the plate cylinder. It will be understood thatapplication of relatively thin printing forms will induce a considerableeconomy of 25-40%. Moreover, not only a reduction of cost but also abetter printing quality in case of printing on relatively roughmaterials is achieved.

A particularly advantageous embodiment of the printing form attachmentmeans of the invention is characterized in that reference markers arepresent on the photopolymeric printing form attachment layer and/or thesupport layer and are visible through the transparent printing formattachment layer. Advantageously the transparent characteristics of thephotopolymeric material for positioning the printing form in the correctposition on the plate cylinder are utilized herein. In this waypositioning the printing form(s) on the plate cylinder can take placerapidly and precisely, no expensive auxiliary apparatus (such as forexample disclosed in EP 0 313 510) for recording different printingforms on subsequent plate cylinders being necessary.

The invention will be explained more in detail by means of the drawings,which illustrate highly schematically an exemplary embodiment of theprinting form attachment means of the invention.

FIG. 1 represents a perspective view of the end of a sheet of anembodiment of the printing form attachment means of the inventionapplied to a roll (not shown).

FIG. 2 represents a perspective view of the one end of a plate cylinder,on which a printing form by means of a piece of printing form attachmentmeans of FIG. 1 is applied.

In FIG. 1 the end of a sheet of the printing form attachment means 1 isillustrated in a perspective view on a much enlarged scale. It will beunderstood that in a practical embodiment the printing form attachmentmeans 1 will have a considerably higher width than the width shown inFIG. 1. The printing form attachment means 1 includes a flexiblesupporting or stabilizing layer 2 consisting of e.g. a polyestermaterial. This supporting layer supports a photopolymeric layer 3covered by a protective layer 4. For example, this protective layer 4can consist of polyester as well. In the exemplary embodimentillustrated in FIG. 1 the supporting layer 2 is provided on both sideswith an adherent layer 5 and 6 respectively, the adherent layer 5connecting the photopolymeric layer 3 with the supporting layer 2 andthe adherent layer 6 serving to attach the printing form attachmentmeans 1 on a plate cylinder partly visible in FIG. 2. Alternatively thesupporting layer 2 can be embodied without the adherent layers 5, 6, thephotopolymeric layer being united with the supporting layer 2 in anotherway and the printing form attachment means being attached on the platecylinder 7 in another way, e.g. by a commonly used double-sided adhesivetape.

In a convenient embodiment of the protective layer 4 a separateprotective layer for the adherent 6 can be omitted when the printingform attachment means 1 is supplied on a roll. Alternatively it is ofcourse possible to apply a separate removable protective layer on theadherent layer 6.

When applying the photopolymeric layer 3 in the printing form attachmentmeans 1 as described above the characteristic of the photopolymericmaterial being sticky or adherent is utilized advantageously.

In case of application of photopolymeric material for producingflexographic printing forms in a conventional way, for example U.S. Pat.No. 3,210,187, after washing out the printing form a subsequenttreatment of the printing form is carried out in order to dissolve thestickiness of the exposed photopolymeric material. The present inventionrelies on the recognition that this sticky or adherent characteristic ofphotopolymeric material makes a photopolymeric layer particularlysuitable for use as an adherent layer in printing form attachment meansas described above. The photopolymeric layer 3 is exposed completely,which results in a further changing of the structure of thephotopolymer.

In FIG. 2 the one end of the plate cylinder 7, on which a piece of theprinting form attachment means 1 of FIG. 1 is applied, is illustrated ina perspective view. The photopolymeric layer 3 is partially broken awayso that the supporting layer 2 is partially visible. Furthermore aprinting form 8 is illustrated, on which highly schematically pictures 9and text 10 are indicated. This printing form 8 is itself embodied in aconventional way with a photopolymeric layer and a supporting layer, onwhich pictures 9 and text 10 are shaped by way of exposure through afilm, then washing out and finally a subsequent treatment in thephotopolymeric layer.

Due to the use of the completely exposed photopolymeric layer 3, theprinting form attachment means 1 as described above has the advantagethat on the one hand the printing form 8 can be attached correctly uponthe plate cylinder 7 and on the other hand it can easily be removed aswell. In this way no residual material remains on the supporting layer 8of the printing form so that this printing form 8 needs not undergo anyspecial cleansing operation and does not damage. As a result theprinting form 8 maintains its availability for repeat orders.Furthermore the printing form attachment means 1 has the advantage thatwhen removing the printing form 8 the photopolymeric layer 3 does notget damaged so that the printing form attachment means has a longlifetime. Experiments have shown that this lifetime amounts at least to8 or 12 months. For the user of the printing form attachment means ofthe invention this means a considerable economy, since when using aconventional printing form attachment means it generally has to bereplaced after removal of a printing form one or more times, whereas asa result of the remaining of glue residues on the printing form itmostly has to be thrown away.

As appears from the drawings the photopolymeric layer 3 has aconsiderable thickness with respect to the adherent layers 5, 6. Thisresults in advantageous utilization of the resilient characteristic ofthe photopolymeric layer 3, as a consequence of which the non-circularshape of the plate cylinder and the bearings of the plate cylinder canbe taken away and a considerable noise reduction and a lifetime increaseof the printing press are achieved. Moreover a relatively resilientsupport of the printing form 8 is realized, which increases the lifetimeof the printing form. The quality of the printed matter is alsoimproved, particularly in case of printing on rough material.

Furthermore, the use of a relatively thick photopolymeric layer 3 on theprinting form attachment means 1 has the advantage that the thickness ofthe printing form 8 itself can be less so that a considerable economy of25 to 40% on material costs for producing the printing forms can berealized.

As indicated schematically in FIGS. 1 and 2 reference markers 11 areprovided to the photopolymeric layer 3 so that before applying theprinting forms on the plate cylinder after applying the printing formattachment means 1 upon the plate cylinder 7 reference markers forpositioning the printing forms are available. In this way the user canrapidly and precisely locate printing forms on the desired place.Alternatively it is possible to print the reference markers 11 on thesupporting layer 2 in case of a suitable embodiment of the connectionbetween the supporting layer and the photopolymeric layer.

The photopolymeric layer 3 can have various thicknesses ranging frome.g. 1 to 4 mm, dependent on the desire of the user. The thickness to beapplied is dependent on the required height of the printing form for therelative printing press. The photopolymeric material has the advantagethat it is resistant to the solvents present in the used inks, as wellas to the influence of ozone.

Although in the foregoing the invention is explained by means of anapplication for attaching printing forms on a print cylinder it will beunderstood that the printing form attachment means of the invention canalso be used for mounting and positioning of characters, numbers andpictures on other printing apparatus, amongst which encoding apparatus,stamping apparatus etc.

Furthermore it has to be noted that for applying the printing formattachment means on a magnetic plate cylinder the printing formattachment means can be provided with a thin metallic sheet.Alternatively the printing form attachment means can be laminated with amagnetic foil. It should be remarked here that it is known per se fromDE-A-2 848 830 to attach a printing plat magnetically to a magneticplate cylinder. The present embodiment, however, contemplates to attachthe printing plate attachment means magnetically to a plate cylinder andto attach the printing plate subsequently to the photopolymeric printingplate attachment means already present on the plate cylinder. Printingplates themselves therefore do not need magnetic or magnetizable layers.

I claim:
 1. Printing form attachment means (1) for removably attaching aflexographic printing form (8) made of a photopolymeric material byadhesion on a plate cylinder (7) of a printing press, characterized inthat the printing form attachment means (1) comprises a completelyexposed photopolymeric printing form attachment layer (3) made of aphotopolymeric material adapted to be located on the plate cylinder (7)for removable adherent attachment of the printing form (8) to the platecylinder (7) utilizing the adherent and sticky characteristics of thephotopolymeric material, as well as a flexible support layer (2) whichsupports the photopolymeric printing form attachment layer (3). 2.Printing form attachment means (1) according to claim 1, characterizedin that the photopolymeric printing form attachment layer (3) has athickness of 1-4 mm.
 3. Printing form attachment means (1) according toclaim 2, characterized in that the printing form attachment layer (3)has a thickness of at least 1.5 mm.
 4. Printing form attachment means(1) according to claim 1, characterized in that reference markers (11)are present on the photopolymeric printing form attachment layer (3)and/or the support layer (2) which is visible through the transparentprinting form attachment layer (3).
 5. Printing form attachment means(1) according to claim 1, characterized in that the support layer (2) isprovided on the side opposite to the photopolymeric printing formattachment layer (3) with a further adherent layer (6) for removablyattaching the printing form attachment means (1) on a plate cylinder ofa printing press.
 6. Printing form attachment means (1) according toclaim 1, characterized in that a thin metallic sheet is provided forremovably attaching the printing form attachment means on a platecylinder (7) of a printing press.
 7. Printing form attachment means (1)according to claim 1, characterized by a thin magnetic foil forremovably attaching the printing form attachment means (1) on a platecylinder (7) of a printing press.
 8. Method for producing a printingform attachment means (1) according to claim 1, wherein an adherentphotopolymeric layer (3) for the removable attachment of the printingform is applied to a support layer (2), characterized in that thephotopolymeric layer (3) is completely exposed.